1. Field of the Invention
The present invention relates to an electrolytic silver recovery system for recovering silver from photographic fixing solutions.
2. Description of the prior art
In 1931, K. Hickman, C. Sanford and W. Weyerts describe in the JSPE, Vol. 17, p. 568-590 a technique for "The electrolytic regeneration of fixing baths". This was the first practical technique to provide for high-efficiency removal of silver from and reuse of the fixing bath.
Passage of an electric current through exhausted fixing bath in a cell provided with a cathode and an anode leads to the deposition of silver on the cathode. Adequate control of the electrolytic process not only enables the silver to be recovered economically, but also allows the fixing solution to be used over and over again, with occasional replenishment to compensate for fixing solution i.e., hypo carried among on the films removed from the bath.
In the performance of the above method, it was found that the operational lifetime of the pump or pumps that maintain a circulation of fixing solution through the cell, and/or also between the cell and the fixing tank of the processor, is seriously affected by the presence of silver particles in the liquid. It is believed that these particles arise from the cathode of the silver recovery cell where they become detached from the deposited silver layer under the influence of vibration, bad adhesion, etc. These particles are attracted to the impeller shaft of the pumps and damage thereby the bearing sleeve or the seal of the pumps which causes leakage of the pumps.
Filters in the liquid circuit upstream of the pumps operate not very satisfactorily because the troublesome silver particles are very fine so that they pass through the filter, whereas the coarser particles and any gelatin tend to prematurely clog the filter.